Multifunction Electrode (MFE) pads are widely used in the treatment and diagnosis of cardiac ailments. Health care professionals and other first-aid providers use MFE pads to monitor the electrical potential during a heartbeat, to provide high-energy electrical stimulation for defibrillation, and to provide lower level electrical stimulation for pacing. Prior to the development of such pads, care providers were required to apply multiple types of pads and possibly use other means of transferring electric current to the patient (i.e., paddles). As one can easily imagine, the use of multiple electrodes along with the use of other devices leads to potential errors and further injury when implemented during an emergency situation.
The creation of a true MFE pad requires designers to balance many factors, not the least of which is price, since the pads are single-use only. A modern MFE pad must be able to transfer short bursts of significant electrical energy while being able to dissipate such energy quickly so that monitoring remains unaffected. MFE pads must also evenly distribute energy across the surface of the pad to reduce the likelihood of burning a patient wearing the pad. Additionally, MFE pads must remain transparent to x-ray transmissions to allow for diagnostic imaging without removal of the pads.
MFE pads contain at least three layers used to effect the transfer of electrical energy between an electrical device and the patient. An electrode layer is located between a layer of protective outer foam and a layer of conductive gel. The conductive gel ensures contact between the electrode layer and the patient's body. The layer of foam, sized to be larger than the electrode layer, is added to cover the electrode and gel layers. The added size allows the foam to extend beyond the periphery of the other two layers to insulate and protect the electrode and gel layers while adding additional adhesive capacity around the periphery of the pad.
The conductive gel spans the distance between the electrode layer and the patient's body. The gel functions to wet the patient's skin making it more accepting to the flow of electrical energy. The physical properties of the gel also help to ensure contact over the entire surface of the exposed gel to distribute the energy being transferred. Lastly, the gel functions as an adhesive helping to ensure that distributed contact with the patient is maintained.
The electrode layer often includes a metal/metal chloride film adhered to a carbon-filled polymer sheet, which is typically a carbon-filled polyvinyl chloride (PVC). The sheet helps to support the metal/metal chloride film. The metal is the primary conductor of the electric energy across the pad while the chloride of the metal allows for the conduction of electrical energy from the electrode to the gel.
The ability of an MFE pad to dissipate energy quickly has come under significant scrutiny. The American National Standards Institute (ANSI) along with the Association for the Advancement of Medical Instrumentation (AAMI) publishes standards for the testing and performance of MFE pads. In particular, a standard known as ANSI/AAMI DF2:1996 was developed to standardize the performance testing of MFE pads and to provide target or allowable limits for the accumulation of DC offset potential measured across a pair of MFE pads.
A measure of an MFE pad's DC offset potential is a measure of the pad's ability to provide energy transfer while retaining the capability to monitor. Electrode pairs store energy by effectively forming a capacitor with the metal layer forming one plate of the capacitor, the human body forming another plate of the capacitor, and the hydrogel forming the dielectric material between the plates. This energy buildup can be seen as a residual voltage between periods of electric energy transfer from the electrode to the patient. This residual voltage or “DC offset potential” has a negative effect of skewing or masking electric signals being generated by the patient's nervous system being monitored through the electrode. Therefore, the lower the DC offset potential the better.
ANSI/AAMI DF2:1996 requires that the DC offset potential across a pair of MFE pads remain less than 400 mV during 60 minutes of pacing, where pacing includes 170, 20 millisecond pulses of 200 mA every minute. While most of the pads currently available continue to fail this standard, one pad, a Philips M3718A, appears to meet these requirements. The construction of this MFE pad is disclosed in U.S. Pat. No. 6,600,957, the entirety of which is incorporated herein by reference.
Current knowledge in the art indicates that the only way to meet the requirements of ANSI/AAMI DF2:1996 is to make the layer extremely thick when compared to others in the prior art. For example, U.S. Pat. No. 6,600,957, discloses that the metal/metal chloride coating of a successful MFE pad design must be “considerably thicker by a factor of six in order to enable the electrode to meet certain pacing requirements which the prior devices are unable to meet.” This metal/metal chloride film of the electrode layer is very expensive to create and apply. Therefore, MFE pads containing such thick layers are very costly, especially for a disposable item.
The current financial crisis affecting the medical care systems around the world can hardly afford the use of expensive MFE pads incorporating a larger amount of expensive components, especially in a disposable product. However, heath care providers should be able to purchase MFE pads that meet the standards currently outlined in ANSI/AAMI DF2:1996 for the safety it offers to the people in need of safe cardiac treatment and care. To date, no such low-cost MFE pad is available.